Tech Talk - Using Black Light to Detect Rodent Evidence - Copesan (2023)

Tech Talk - Using Black Light to Detect Rodent Evidence - Copesan (1)By William Kolbe, BCE

The amino acids in rodent urine and hair will fluoresce (shine) when exposed to certain wavelengths of light found in black light, commonly referred to as ultraviolet light. Black light shines a deep blue and often is used with artistic poster displays. Other substances like starch, bleached sack fibers, optical bleaches, glues and adhesives, dyes, some cleaning agents, and many industrial chemicals also will fluoresce, so care and practice is needed to effectively use this inspection and diagnostic tool as a PMP.

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Rodents are incontinent. This means they defecate and urinate as they move about constantly. Unlike humans, as soon as the rodent body produces excreta, it is expelled. Pest control practitioners know most urine and droppings are deposited where the rodents spend most of their time and where they travel. A visual inspection using a flashlight will often reveal rodent droppings, urine staining and other evidence. The black light can be used to corroborate suspected contamination and rodent presence.

After visually identifying likely rodent entry points along a structure’s perimeter, use a black light to determine if it is indeed being used as a runway. Black light inspection of premises is less accurate as dust, dirt, debris and cleaning agents can obscure urine fluorescence. The light is most effective for inspecting packages, stored materials and bagged goods.

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  • Rechargeable black lights should be fully charged when used, to allow for the strongest possible illumination.
  • Black lights should be used in dark, or subdued lighting locations. If practical, turn overhead lights down, or move goods being inspected to darker, less well-lit areas.
  • Move the black light unit over the surface being examined, holding it as close as possible without damaging the unit.
  • Hold the light at an angle, allowing visual observations to be made.
  • Urine staining is most likely found between boxes and bags.


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  • Rodent urine fluoresces blue-white to yellow-white when dry, bluer when fresh and becoming paler with age.
  • Rodent hair fluoresces blue-white.
  • Starches, detergents and soaps show as a brilliant blue-white stain.
  • Bleached fibers in sacking looks blue-white.
  • Pitches and tars look yellow.
  • Glues used to seal cardboard boxes radiate a mustard yellow color.
  • Human urine looks like rodent urine, but will be present over larger areas.
  • Lubrication oils and grease fluoresces green-white to blue-white to brown.
  • Rodent urine often will appear as a thin line of dots, drops or streaks running between cartons and bags, especially on vertical surfaces.
  • Rodent urine often will have tail drag marks through the fluorescing deposit.
  • Rodent urine has little to no symmetry to its deposit. If a deposit appears large, patchy and evenly distributed, it’s not rodent urine.

PRACTICE MAKES PERFECT!Practice using the black light on pieces of cardboard or packaging known to have been in contact with rodents. You also could visit a pet store and ask the manager if you can practice near the pet mice or rat containers (before or after hours of course). You might land a contract checking for rodent escapees!

Use the black light on cartons and bags known to come from uninfested areas and cardboard known to have been exposed to bleach, glues and other chemicals to become accustomed to what other materials and chemicals look like when fluorescing.

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LIMITATIONS AS A TOOL.Understand black lights have limitations as a tool. Black light urine evidence should be used as a first indicator of possible rodent contamination, or to corroborate other suspected evidence. It shouldn’t be used as a stand-alone, diagnostic tool to reject goods as we know other substances fluoresce.

Kolbe is the director of technical and training services, Viking Pest Control, Bridgewater, N.J. His career in pest management started in June 1974 after graduating from the University of Delaware.

This Tech Talk article was originally published in the September 2016 edition ofPCT magazine.


Can a black light detect mice? ›

The detection of rodent contamination by black light is based on the phenomenon of rodent urine showing blue-white to yellow-white fluorescence when viewed under black light. The fresher the stain the more blue will fluoresce. Urine stains on food bags, containers, floors, etc.

Can UV light detect rat urine? ›

U.V (black light) is an ideal pocket tool for tracking rodent urine; helping to find entrance points and runways. Whilst invisible in normal light, urine stains on food bags, containers, floors etc is more noticeable under UV. The fresher the stain, the more the light will fluoresce.

What can a black light detect? ›

Black lights, also known as ultraviolet lights (UV), are often used in professional cleaning to help detect if hidden pathogens are present on walls, high-touch areas, ledges, furniture, and scores of other surfaces.

Can rodents see UV light? ›

In the first clear evidence of ultraviolet vision in mammals, Dr. Gerald H. Jacobs and his colleagues at the University of California in Santa Barbara have discovered that house mice, gerbils, gophers and rats have photoreceptors more sensitive to ultraviolet light than to any other light on the spectrum.

How do you use UV light for pest control? ›

The UV light is used as bait to attract the insect to the machine. Once the insects are in close proximity, a high voltage grid or electrified mesh located just in front of the UV lights electrocutes or “zaps” the insects dead. Some devices utilise glue boards to catch insects rather than electrocute them.

What is the best way to track mice? ›

Tracks and footprints: layout talcum powder or flour on the floor to see if there are any mouse tracks or footprints. These are usually small and depending on the type of rodent, will have between four and five toes on the legs. Droppings: mouse droppings are a clear sign of a mouse infestation in your home.

Does animal urine show up under a blacklight? ›

Wavelengths in a blacklight cause phosphorous and proteins in the urine to glow, making it easier to spot old stains. Pet stains that weren't cleaned properly with an enzyme-based cleaner will show up under UV light as well.

Does poop show up under a blacklight? ›

Just as human body secretions are visible under a black light, so are the urine, feces and other body secretions of animals. Black lights are useful for finding the unknown location of pet urine odors and for finding evidence of rats or mice lurking in your home.

What animals urine glows under black light? ›

Cat urine, in particular, glows very brightly under ultraviolet light. Urine glows under a black light primarily because it contains the element phosphorus.

What's the difference between a blacklight and a UV blacklight? ›

The most crucial difference between these two types of light is their wavelength, with ultraviolet having a shorter wavelength than a blacklight. The ultraviolet spectrum extends from 100 nanometers (nm) to 400 nm, whereas the blacklight spectrum is between 225 and 395 nanometers.

What color shows up on Blacklight? ›

WHICH COLORS GLOW UNDER BLACK LIGHTS? When selecting what to wear for a black light party you want to find glow party outfits and materials that are either white or fluorescent. The brighter the neon color the greater the chance that the item will glow. Fluorescent green, pink, yellow, and orange are the safest bets.

Can I use my phone as a black light? ›

While no smartphone is technically capable of emitting UV light currently, you can mimic the effect of a black light using your phone's LED flash, a few markers, and some transparent tape.

Do lights keep rodents away? ›

Unfortunately, the light inside your house is not a very effective deterrent to mice. Once inside a house or a building, they can easily look for dark areas to hide until such time as all lights are turned off. Places they can hide include inside the walls, crawl spaces, attics, and ceilings.

Can rodents see infrared light? ›

Humans and mice, like other mammals, cannot see infrared light, which has wavelengths slightly longer than red light — between 700 nanometres and 1 millimetre.

What color light do rats not see? ›

Rodents lack red cones (Deegan and Jacobs, 1993; Jacobs et al., 1991; Szél and Röhlich, 1992), but from the inability to see red as a color, it does not necessarily follow that they cannot absorb red light through their rod-dominated retina to support form vision.

Are bugs attracted to UV black light? ›

It has been well documented in the literature that light in the ultraviolet (UV) range is attractive to flies and other insects (e.g., Hollingsworth et al. 1968), but it was Thimijan and Pickens (1973) who found that wavelengths between 310 and 370 nm are the most attractive to house flies, Musca domestica L.

What bugs are attracted to UV light? ›

Traps using UV light bulbs attract fungus gnats, fruit flies, and phorid flies, making them suitable for indoor use.

How do you place an ultrasonic pest repeller? ›

Once you've identified an area with rodent activity, plug the unit into an outlet that is open to the rest of the room, not behind furniture where the sound waves may be blocked. Note, hard surfaces reflect ultrasound, while soft surfaces absorb it.

How do you get rid of mice when you don't know where they're coming from? ›

7 tips to get rid of mice
  1. Get a cat. If no one in your family has a cat allergy, getting a cat might just be the easiest way to get rid of mice. ...
  2. Use essential oils. ...
  3. Set humane traps. ...
  4. Try a hot pepper solution. ...
  5. Build your own humane trap. ...
  6. Pack spaces with steel wool. ...
  7. Block with duct tape.

How do professionals get rid of mice? ›

Expect to see baited traps in these areas as well as rodent poison. Rodenticide correctly deployed on the exterior of a house may be the preferred method for getting rid of mice. Traps are effective solutions, but the correct use of rodenticides is best for complete extermination.

How do you find a hidden mouse in your house? ›

Chewed holes in kitchen cabinets, baseboards, drawers, etc. Holes in food packaging. Scratching, gnawing or scampering noises inside wall voids. Tiny footprints in spilled flour or other material.

What color is rat urine under black light? ›


Rodent urine fluoresces blue-white to yellow-white when dry, bluer when fresh and becoming paler with age. Rodent hair fluoresces blue-white.

What glows purple under black light? ›

Plastics Glow Under Black Light

For example, neon-colored acrylic may contain fluorescent molecules. Other types of plastic are less obvious. Plastic water bottles usually glow blue or violet under ultraviolet light.

Is there a blacklight app for iPhone? ›

Black Light Vision create the black light effect through the iPhone camera.

Does female discharge glow under black light? ›

Since body fluids like semen, saliva, and vaginal fluids are naturally fluorescent, the use of a light source offers a unique method for locating them.

What pee looks like under blacklight? ›

However, keep in mind that urine will not, as many believe, show up bright white under a blacklight. Instead, it will be a bright yellow. Some people find it easier to spot urine with a blacklight at night.

Why does black light still show urine after cleaning? ›

see less The glow visible under black lights is from the phosphorus in urine. While enzymes can break down urea (the main molecule that makes urine smell), you can't break down phosphorous because it's an atom. So, an area can be completely odor-free, and still glow under a blacklight.

What color is rodent urine? ›

The color of normal rodent urine varies from colorless to yellowish-white to light brown. Always consider color and turbidity in association with urine-specific gravity.

What kind of light detect pet urine? ›

UV STAIN DETECTIVE is a simple to use and highly effective Blacklight Flashlight. Any dry pet urine is detected quickly and easily. The favorite spots for your cat or dog to pee cannot be detected by the naked eye but UV Stain Detective tracks them down fast!

Do you need glasses to use a blacklight? ›

Anyone using an ultraviolet lamp should wear a pair of UV-blocking glasses to protect the eyes. Ultraviolet light can cause eye irritation or damage. These glasses are recommended for use with the M12 Ultraviolet Flashlight and Lamp. They are made of polycarbonate, the most commonly used material in safety eyewear.

What do things look like under a blacklight? ›

The ultraviolet light emitted by blacklight is absorbed by fluorescent substances and re-emitted, making a wavelength of light visible longer and the fluorescent items look as if they are glowing. Blacklights are common at parties and nightclubs, where white items will glow especially brightly.

Can I use a black light instead of a UV light? ›

In sterilization and filtering applications, black light doesn't have the same power that UV light has, though it does make white clothing look pretty cool in the dark.

What color light can mice not see? ›

Mice are dichromats that only possess short- and medium-wavelength-sensitive cones. They dont see red light; they only see blue and green light, similar to a person with red-green color blindness.

Will mice avoid a room with lights on? ›

Unfortunately, the light inside your house is not a very effective deterrent to mice. Once inside a house or a building, they can easily look for dark areas to hide until such time as all lights are turned off. Places they can hide include inside the walls, crawl spaces, attics, and ceilings.

Do mice like dark light? ›

Mice are nocturnal creatures, so they are most active between dusk and dawn. They don't usually like bright lights, but a mouse may sometimes be seen during the day, especially if its nest has been disturbed or it is seeking food. Seeing them in the day also can indicate a large infestation in a home.

Can mice detect infrared light? ›

Humans and mice, like other mammals, cannot see infrared light, which has wavelengths slightly longer than red light — between 700 nanometres and 1 millimetre.

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